102 lines
3.2 KiB
Go
102 lines
3.2 KiB
Go
package edidpatcher
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import (
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"fmt"
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"github.com/charmbracelet/log"
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"github.com/google/uuid"
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)
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// Calculates a checksum for a given EDID block (base EDID, extension blocks, etc.)
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func CalculateEDIDChecksum(edidBlock []byte) byte {
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sum := 0
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for _, value := range edidBlock[:len(edidBlock)-1] {
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sum += int(value)
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}
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return byte((-sum) & 0xFF)
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}
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var MSFTPayloadSize = byte(22 + 4)
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// Patch a given EDID to be a "specialized display", allowing for the display to be used by third-party window-managers/compositors/applications directly.
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func PatchEDIDToBeSpecialized(edid []byte) ([]byte, error) {
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newEDID := make([]byte, len(edid))
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copy(newEDID, edid)
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isAnEnhancedEDID := len(newEDID) > 128
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foundExtensionBase := 0
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extensionBaseExists := false
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// Find an appropriate extension base
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if isAnEnhancedEDID {
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for currentExtensionPosition := 128; currentExtensionPosition < len(newEDID); currentExtensionPosition += 128 {
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if newEDID[currentExtensionPosition] != 0x02 {
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continue
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}
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if newEDID[currentExtensionPosition+1] != 0x03 {
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log.Warn("Incompatible version detected for ANSI CTA data section in EDID")
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}
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foundExtensionBase = currentExtensionPosition
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extensionBaseExists = true
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}
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if foundExtensionBase == 0 {
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foundExtensionBase = len(newEDID)
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newEDID = append(newEDID, make([]byte, 128)...)
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}
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} else {
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foundExtensionBase = 128
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newEDID = append(newEDID, make([]byte, 128)...)
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}
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newEDID[foundExtensionBase+2] = MSFTPayloadSize
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if !extensionBaseExists {
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// Add another extension to the original EDID
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if newEDID[126] == 255 {
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return nil, fmt.Errorf("EDID extension block limit reached, but we need to add another extension")
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}
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newEDID[126] += 1
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newEDID[127] = CalculateEDIDChecksum(newEDID[:128])
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newEDID[foundExtensionBase] = 0x02
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newEDID[foundExtensionBase+1] = 0x03
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newEDID[foundExtensionBase+3] = 0x00
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} else {
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if newEDID[foundExtensionBase+2] != MSFTPayloadSize && newEDID[foundExtensionBase+2] != 0 {
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currentBase := newEDID[foundExtensionBase+2]
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copy(newEDID[foundExtensionBase+4:foundExtensionBase+int(currentBase)-1], make([]byte, int(currentBase)-1))
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copy(newEDID[foundExtensionBase+int(MSFTPayloadSize):foundExtensionBase+127], newEDID[foundExtensionBase+int(currentBase):foundExtensionBase+127])
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}
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}
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generatedUUID := uuid.New()
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uuidBytes, err := generatedUUID.MarshalBinary()
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if err != nil {
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return nil, fmt.Errorf("failed to marshal UUID: %w", err)
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}
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// Implemented using https://learn.microsoft.com/en-us/windows-hardware/drivers/display/specialized-monitors-edid-extension
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// VST & Length
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newEDID[foundExtensionBase+4] = 0x3<<5 | 0x15 // 0x3: vendor specific tag; 0x15: length
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// Assigned IEEE OUI
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newEDID[foundExtensionBase+5] = 0x5C
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newEDID[foundExtensionBase+6] = 0x12
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newEDID[foundExtensionBase+7] = 0xCA
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// Actual data
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newEDID[foundExtensionBase+8] = 0x2 // Using version 0x2 for better compatibility
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newEDID[foundExtensionBase+9] = 0x7 // Using VR tag for better compatibility even though it probably doesn't matter
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copy(newEDID[foundExtensionBase+10:foundExtensionBase+10+16], uuidBytes)
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newEDID[foundExtensionBase+127] = CalculateEDIDChecksum(newEDID[foundExtensionBase : foundExtensionBase+127])
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return newEDID, nil
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}
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